1. Field of the Invention
According to the present invention there is provided a process for the acceleration of the setting of hydraulic binding agents such as cement and mortar and concrete prepared thereof. Possibilities for using this process are the preparation of prefabricated elements and the acceleration of concrete prepared at the construction site. In the former it may be used to shorten or even to eliminate the usual hardening acceleration by heat (electrical heating or oil heating or steam). In the latter the time for stripping the forms of the concrete may be shortened, or it is also possible to build with concrete at low temperature.
In all these cases the process of this invention shows remarkable economical advantages. A special field of the application is the spray mortar and the spray concrete.
Such mortars and concretes are used for the preparation of buildings of any structure above or below the ground as well as for the completion and the coating of subterranean, natural or artificial cavities, such as gallery-, tunnel- or mining-constructions, where the concrete must satisfy the statical requirements, and where the concrete must be waterproof. Such mortars and concretes are also used for the consolidation of excavations, slopes, loose rock walls etc.
2. Description of the Prior Art
There are already known many substances which accelerate the setting and the hardening of concrete: The most frequently used substances are among others the strong alkali reactive substances such as alkali hydroxides, alkali carbonates, alkali silicates, alkali aluminates and earth alkali chlorides.
The strong alkali reactive substances are accompanied with undesirable annoyances of the manufacturer. Such products may be very corrosive to the skin and may cause inflammations of the eyes, which may injure the strength of vision. By inhaling the dust produced by the work up of these products also harmful consequences to the respiratory organs may be caused.
Seen from the technological standpoint of the concrete the strong alkali setting accelerators reduce the end stability and increase the shrinkage, which may lead to the formation of cracks and which, therefore, calls in question the permanence of a building.
As a rule, the chloride containing setting accelerators are not desired at the construction site because they may lead to corrosion of the reinforcing bars in the concrete as well as of the equipment used at the construction site.
Furthermore, it is known that the chloride containing setting accelerators strongly reduce the stability against chemicals, especially the sulfate stability of the concrete.